THK NUNMKTALLIC MINKRALS. 169 



lino motamoi'phic rocks, l)oth silicoous iind calcaivous, soiiiotiincs in 

 the form of disseminated scales, as in the ciTstalline limestone of Essex 

 County, New York (Specimen No. ;nS2r), T.S.N.M), or in em])edded 

 masses, streaks, and lumps, often of such dimensions that sinj^-le blocks 

 of several hundred pounds weight are obtainable. (Specimen No. 

 5Jt97(), U.S.N.M.) It is also found in the form of veins. 



The fact that the mineral is carbon, one of the constituents of animal 

 and veo-etable lif«\ has led many authorities to regard it, like coal, as 

 of vegetable origin. While this view is very plausible it can not, how- 

 ever, be regarded as in all cases proven. 



That graphite may l)e formed independently of organic life is shown 

 by its presence in cast iron, where it has crystalized out, on cooling, 

 in the form of In-ight metallic scales. See Specimens Nos. 51298 and 

 51312 in the metallurgical series of the manufacture of iron. 



Cai'bon is also found in meteorites which are plainly of igneous 

 origin, and which have thus far yielded no certain traces of either 

 plant or animal organisms. It is, however, a well-known fact that 

 coal— itself of organic origin — has in some cases been converted into 

 graphite through metamorphic agencies, and intermediate stages like 

 the graphitic anthracite of Newport, Rhode Island, afford good illus- 

 trations of such transitions. (Specimen No. 59099, U. S. N .M.) Certain 

 European authorities^ have shown that amorphous carbonaceous par- 

 ticles in clay slates have l)een converted into graphite by the metamor- 

 phosing influence of intruded igneous rocks. Prof. J. S. Newberry 

 descril>ed an occurrence of this nature in the coal fields of Sonora, 

 Mexico.'^ He says: 



All the western portion of this coal field seems to be much broken liy trap dikes 

 which have everywhere metamorphosed the coal and converted it into anthracite. 

 At the locality examined the metamorphic action has been extreme, converting 

 most of the coal into a brilliant ))ut somewhat friable anthracite, containing li or 4 

 per cent of volatile matter. At an outcrop of one of the beds, however, the coal was 

 found converted into graphite, which has a laminated structure, but is unctuous to 

 the touch and marks paper like a lead pencil. The metamorphism is much more 

 comiilete than at Newport (Rhode Island) [Specimen No. 59099, U.S.N.M.], furnishing 

 the best exami)le yet known to me of the conversion of a bed of coal into graphite. 



In New York State, and in Canada, graphite occurs in Laurentian 

 rocks, hoth in beds and in v(Mns, a portion of the latter being appar- 

 ently true tissure veins and others shrinkage cracks or segregation veins 

 which traverse in countless numbers the containing rocks. It is said'' 

 I hat in the Canadian regions (Specimens Nos. 51007, 59976, U.S.N.M.), 

 the deposits occur generally in limestone or in their immediate vicinity, 

 and that granular varieties of the rock often contain large crystalline 



'Beck and Luzi, Berichte der Deutschen Chemischen Gesellschaft, 1891, p. 24. 



•■'School of Mines Quarterly, VIII, 1887, p. 334. 



^ See On the Graphite of the Laurentian of Canada, by J. W. Dawson, Proceedings 

 of the Geological Society of London, XXV, 1870, p. 112, and an article on Graphite 

 by Prof. J. F. Kemp in The Mineral Industry, II, 1893, p. 335. 



